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When a `?` operation requires an `Into` conversion with additional bounds (like having a concrete error but wanting to convert to a trait object), we handle it speficically and provide the same kind of information we give other `?` related errors.
```
error[E0277]: `?` couldn't convert the error: `E: std::error::Error` is not satisfied
--> $DIR/bad-question-mark-on-trait-object.rs:5:13
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LL | fn foo() -> Result<(), Box<dyn std::error::Error>> {
| -------------------------------------- required `E: std::error::Error` because of this
LL | Ok(bar()?)
| ^ the trait `std::error::Error` is not implemented for `E`
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= note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
= note: required for `Box<dyn std::error::Error>` to implement `From<E>`
```
Avoid talking about `FromResidual` when other more relevant information is being given, particularly from `rust_on_unimplemented`.
40 lines
1.9 KiB
Plaintext
40 lines
1.9 KiB
Plaintext
error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
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--> $DIR/try-on-option-diagnostics.rs:7:6
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LL | fn a_function() -> u32 {
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| ---------------------- this function should return `Result` or `Option` to accept `?`
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LL | let x: Option<u32> = None;
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LL | x?;
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| ^ cannot use the `?` operator in a function that returns `u32`
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error[E0277]: the `?` operator can only be used in a closure that returns `Result` or `Option` (or another type that implements `FromResidual`)
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--> $DIR/try-on-option-diagnostics.rs:14:10
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LL | let a_closure = || {
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| -- this function should return `Result` or `Option` to accept `?`
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LL | let x: Option<u32> = None;
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LL | x?;
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| ^ cannot use the `?` operator in a closure that returns `{integer}`
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error[E0277]: the `?` operator can only be used in a method that returns `Result` or `Option` (or another type that implements `FromResidual`)
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--> $DIR/try-on-option-diagnostics.rs:26:14
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LL | fn a_method() {
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| ------------- this function should return `Result` or `Option` to accept `?`
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LL | let x: Option<u32> = None;
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LL | x?;
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| ^ cannot use the `?` operator in a method that returns `()`
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error[E0277]: the `?` operator can only be used in a trait method that returns `Result` or `Option` (or another type that implements `FromResidual`)
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--> $DIR/try-on-option-diagnostics.rs:39:14
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LL | fn a_trait_method() {
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| ------------------- this function should return `Result` or `Option` to accept `?`
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LL | let x: Option<u32> = None;
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LL | x?;
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| ^ cannot use the `?` operator in a trait method that returns `()`
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error: aborting due to 4 previous errors
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For more information about this error, try `rustc --explain E0277`.
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